1. Technical Field
This disclosure generally relates to an image forming apparatus and a foam application device.
2. Description of the Related Art
A liquid-jet image forming apparatus such as an inkjet recording apparatus uses one or more recording heads that jet liquid droplets (e.g., ink droplets) to form an image. A liquid-jet image forming apparatus is used, for example, for a printer, a facsimile machine, a copier, a plotter, or a multifunction copier having functions of them. Such a liquid-jet image forming apparatus jets liquid droplets from its recording heads onto paper (not limited to a sheet of paper but also refers to any medium, such as an OHP sheet, to which ink droplets or other liquid droplets can adhere, and may also be called a recording medium, recording paper, recording sheet, etc.), and thereby forms (records or prints) an image on the paper. There are roughly two types of liquid-jet image forming apparatuses: a serial-type image forming apparatus including a recording head that jets liquid droplets while moving in the main-scanning direction to form an image; and a line-type image forming apparatus including a line-type recording head that does not move when jetting liquid droplets to form an image.
In the present application, an image forming apparatus refers to an apparatus that forms an image by jetting a liquid onto a recording medium made of paper, thread, fabric, textile, leather, metal, plastic, glass, wood, ceramic, etc. Also, “image forming” indicates not only a process of forming a meaningful image such as a character or a drawing on a recording medium, but also a process of forming a meaningless image such as a pattern on a recording medium (or just jetting liquid droplets onto a recording medium). Further, in the present application, “ink” refers not only to a colored liquid for drawing or printing but also to any substance that is to be jetted in the form of liquid. For example, “ink” may refer to a DNA specimen, a resist, or a pattern material.
There are known problems in forming an image by jetting ink droplets including color materials using a liquid-jet image forming apparatus. Such problems include “feathering” where edges of dots formed by ink droplets become jagged; “color bleeding” where adjacent ink droplets jetted onto paper and having different colors mix together and the color boundaries are blurred; and “long time” necessary for ink droplets jetted onto paper to dry.
Several methods have been developed to solve the above problems. In a method disclosed in patent document 1, a heating unit is used after and/or before printing to prevent bleeding of ink and to accelerate drying of the ink.
[Patent document 1] Japanese Patent Application Publication No. 8-323977
In a method disclosed in patent document 2, a pretreatment liquid that reacts with ink and prevents bleeding is applied by an application roller to paper. Also, in a method disclosed in patent document 3, a pretreatment liquid is applied to paper by jetting a mist of the pretreatment liquid from a liquid-jet head.
[Patent document 2] Japanese Patent Application Publication No. 2002-137378
[Patent document 3] Japanese Patent Application Publication No. 2005-138502
However, adding a heating unit to an image forming apparatus as in patent document 1 increases the power consumption of the image forming apparatus. Meanwhile, with a method of applying a pretreatment liquid using an application roller or a liquid-jet head as disclosed in patent document 2 or 3, it is difficult to evenly apply the pretreatment liquid on paper. Also, the pretreatment liquid takes a long time to dry after reacting with ink on the paper and causes the paper to curl or warp, and this in turn increases the likelihood of paper jam.